Voltage regulators

ABSTRACT

An embodiment of an arrangement includes a voltage regulator configured to provide an output voltage, said voltage regulator configured to receive one of a plurality of different regulator reference voltages and a controller configured to provide a selection signal, said selection signal being used to control which of said regulator reference voltages said voltage regulator receives.

TECHNICAL FIELD

An embodiment relates to voltage regulators.

SUMMARY

Integrated circuits may have different circuit parts which require aknown voltage or current to run as required. In order to provide thisknown voltage or current, a voltage regulator or current regulator isprovided, respectively.

According to an embodiment, an arrangement includes: a voltage regulatorconfigured to provide an output voltage, said voltage regulatorconfigured to receive one of a plurality of different regulatorreference voltages; and a controller configured to provide a selectionsignal, said selection signal being used to control which of saidregulator reference voltages said voltage regulator receives.

According to an embodiment, the controller may include comparisoncircuitry, wherein said comparison circuitry is configured to comparesaid output voltage with at least one controller reference voltage toprovide a comparison output.

According to an embodiment, the controller may include a comparatorconfigured to compare said output voltage with at least one controllerreference voltage.

According to an embodiment, the at least one controller referencevoltage may have a value which is less than said output voltage.

According to an embodiment, the controller reference voltage may have avalue which is within approximately 10 millivolts (mV) of the outputvoltage.

According to an embodiment, the comparison circuitry may be configuredto compare a plurality of different controller reference voltages tosaid output voltage.

According to an embodiment, the controller may include selectioncircuitry configured to receive said comparison output and in response,to select one of said regulator reference voltages.

According to an embodiment, in dependence on said comparison output, anext higher or next lower reference may be selected.

According to an embodiment, the selection circuitry may include acounter.

According to an embodiment, the counter may be configured to select ahigher reference voltage when a count increases or decreases and toselect a lower reference voltage when the count decreases or increases,respectively.

According to an embodiment, the voltage regulator may include adifferential amplifier configured to receive said selected referencevoltage and said output voltage, said differential amplifier configuredto provide an output which is used to control the output voltage.

According to an embodiment, an integrated circuit may include any of theprevious arrangements.

According to an embodiment, a method includes: providing an outputvoltage from a voltage regulator using one of a plurality of differentregulator reference voltages; and providing a selection signal which isused to control which of said regulator reference voltages said voltageregulator receives.

According to an embodiment, the method may include comparing said outputvoltage with at least one controller reference voltage to provide acomparison output.

According to an embodiment, the method may include comparing said outputvoltage with one controller reference voltage.

According to an embodiment, the one controller reference voltage mayhave a value which is less than said output voltage.

According to an embodiment, the controller reference voltage may have avalue which is within approximately 10 mV of the output voltage.

According to an embodiment, the comparing may include comparing aplurality of different controller reference voltages to said outputvoltage.

According to an embodiment, the method may include providing saidcomparison output to regulator-reference-voltage-selection circuitry.

According to an embodiment, the selection circuitry may include acounter and said method may include selecting a higher reference voltagewhen a count increases or decreases and selecting a lower referencevoltage when the count decreases or increases, respectively.

According to an embodiment, the method may include selecting independence on said comparison output, a next higher or next lowerreference.

According to an embodiment, the method may include differentiallyamplifying said selected regulator reference voltage and said outputvoltage to provide an output which is used to control the outputvoltage.

According to an embodiment, an apparatus or arrangement may be providedto perform any of the above methods. The apparatus or arrangement mayinclude a die or integrated circuit.

According to an embodiment, an integrated circuit includes: a voltageregulator configured to provide an output voltage, said voltageregulator configured to receive one of a plurality of differentregulator reference voltages; and a controller configured to provide aselection signal, said selection signal being used to control which ofsaid regulator reference voltages said voltage regulator receives.

According to an embodiment, the integrated circuit may include at leastone capacitor provided on an output of said integrated circuit.

According to an embodiment, an arrangement includes: voltage regulationmeans for providing an output voltage, said voltage regulation means forreceiving one of a plurality of different regulator reference voltages;and control means for providing a selection signal, said selectionsignal for controlling which of said regulator reference voltages saidvoltage regulation means receives.

In the above, many different embodiments have been described. It shouldbe appreciated that further embodiments may be provided by thecombination of any two or more of the embodiments described above, andthat other non-described embodiments may exist.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments are described below, by way of example only, with referenceto the accompanying drawings, in which:

FIG. 1 shows a first voltage regulator arrangement on an integratedcircuit, according to an embodiment.

FIG. 2 shows part of the voltage selection arrangement of FIG. 1,according to an embodiment.

FIG. 3 shows part of the control part of the arrangement of FIG. 1,according to an embodiment.

FIG. 4 shows a second voltage regulator arrangement on an integratedcircuit, according to an embodiment.

FIG. 5 shows a method according to an embodiment.

DETAILED DESCRIPTION

An embodiment will now be described with reference to FIG. 1. A voltageregulator 16 is provided. The voltage regulator 16 is, in someembodiments, provided on an integrated circuit 2. As will be describedin more detail, most of the voltage regulator is provided on theintegrated circuit 2, but a compensation capacitor 22 can be providedexternal to the integrated circuit.

This capacitor 22 is used to assist the stability of the regulator. Thecapacitor 22 is provided on a low-voltage device pin. In the embodimentshown in FIG. 1, one capacitor 22, and hence one pin, are shown. In someembodiments, more than one low-voltage device pin may be provided. Someor each of the low-voltage device pins may be provided with a capacitor.

Some embodiments aim to reduce the value of the one or more externalcapacitors as compared to current proposals. Current proposals usecapacitors with a capacitance in range of approximately 1 uF to 4.7 uF.Some embodiments may be used with a device-pin capacitor in the range ofapproximately 1 uF to 40 uF. It should be appreciated that lower-valuecapacitors may be less expensive than higher-value capacitors.

If the value of a stability capacitor 22 is reduced, then the gain of anon-chip regulator may be limited. If the gain is lower, then the offsetvoltage may have a higher value. Offset voltage is defined as the changein the output voltage Vout when the current Icore in the core changesfrom a minimum value to a maximum value. With smaller chip featuresizes, the supply-voltage range may be limited at the higher side by thethickness of the oxide (e.g., the gate oxide of a transistor). On theother hand, the supply-voltage range may be limited on the lower side bythe threshold voltage of a transistor. With smaller-feature-sizedintegrated circuits, the current consumption may be increased due to anincreased leakage current or increased processing in the core of theintegrated circuit.

In some embodiments, the dc (steady state) offset may be at leastpartially removed. This may ensure that the voltage remains within thesupply-voltage range. This may alternatively or additionally provide amargin for accommodating the current transients.

In some embodiments, the arrangement shown in FIG. 1 may cancel the DCoffset by increasing the reference voltage provided to the regulator bythe offset amount.

In some embodiments, at higher temperatures there may be a constantleakage current inside the device which generates an offset. Thisleakage current is not switching. The arrangement of FIG. 1 may cancelthe DC offset due to the leakage current.

The regulator 16 includes an amplifier 4. In some embodiments, thisamplifier may be a differential amplifier. The amplifier 4 receives at afirst input the output voltage Vout 20. Vout is provided as a feedbackto the input of the amplifier. The amplifier 4 also receives as a secondinput a reference voltage Vref 6.

A capacitance C1 7 is provided between the Vref input of the amplifier 4and ground. The value of Vref 6 is controlled by a transistor array 12.The transistor array 12 is shown in more detail in FIG. 2.

Reference is made to FIG. 2, which shows the transistor array 12 in moredetail. The transistor array 12 includes N transistors. In thisembodiment, N is equal to 8. It should be appreciated that in differentembodiments, N can be greater or less than 8.

N different reference voltages are provided. As N is 8, in this examplethe reference voltages are Ref0 to Ref7. Each reference voltage isrespectively coupled to one end (e.g., a source or a drain) of a channelof a transistor. The transistors are referenced 12 a to 12 h and arerespectively coupled to one of the different reference voltages. Thus,reference voltage Ref0 is coupled to one end of the channel of the firsttransistor 12 a and so on. Each gate of each transistor 12 is arrangedto receive one bit of a seven-bit selection signal 24. This selectionsignal includes one bit at one state and N−1 bits at the other state. Inthis example, as the transistors are NMOS FET transistors, the one bitwill be at the on state “1” and the other bits will be in the off state“0”. Accordingly, all of the N transistors will be off except for one.Accordingly, the reference voltage supplied to the transistor which isturned on will provide the reference voltage Vref. In other words, theother end of the channel of the transistor to which the referencevoltage is coupled will provide the reference Vref if the respectivetransistor is turned on.

In the example shown in FIG. 2, the transistors are NMOS transistors.However it is appreciated that this is by way of example only, and indifferent embodiments different transistors may be used. For example thetransistors may be P-type transistors. Alternatively or additionally,the transistors may be based on an alternative technology to MOSFETs,for example bipolar technology or the like.

The N different voltages may be different from a next higher or nextlower voltage by a discrete voltage step which is constant. For example,the lowest reference voltage value may be x, the next lowest voltagevalue may be x+y, the next voltage value may be x+2y and so on. However,this is by way of example only, and the difference between adjacentreference voltages may vary.

In an embodiment, the step size may be approximately 10 mV. However, thenumber of reference voltages or the step size may be dependent on theapplication.

In an embodiment, the lowest reference voltage may be approximately 1.20V (Ref 0) and the highest reference voltage may be approximately 1.27 V(Ref 7). However, this is by way of example only.

The mechanism for controlling the value of the selection signal will bedescribed in more detail later.

Referring again to FIG. 1, the amplifier 4 provides an output which isused to control the gate of a MOS ballast transistor MB 10. Thetransistor 10 is coupled at one end of its channel to a voltage rail andat the other end provides the output voltage Vout 20. The output voltageis, as mentioned previously, fed back into an input of the amplifier 4.The driving of the PMOS ballast transistor 10 generates power for theintegrated circuit 2 and this is represented schematically by thecurrent generator providing a current Icore 18 for the core. The outputvoltage Vout is output from the integrated circuit 2 and is coupled tothe external stability capacitor Cstab 22 discussed previously.

The differential amplifier is configured to bring the output voltageVout as close as possible to the reference voltage Vref. For this reasonVout is fed back to the input of the differential amplifier. Thedifferential amplifier provides an output which controls the ballasttransistor to act as a resistor, the value of the resistance beingdependent on the output of the amplifier. The feedback of Vout is suchthat the transistor is controlled to have a resistance such that Vouttends to the value of Vref. This part of the circuit provides arelatively fine control of the value of Vout.

The arrangement of FIG. 1 has a control part 24, which is configured toprovide the selection signal discussed previously. In the embodimentshown in FIG. 1, the control part has N comparators 30. However, tosimplify FIG. 1, only one of the comparators 30 is shown. Reference ismade to FIG. 3, which shows in more detail the control part.

In FIG. 3, eight comparators 30 a-30 h are provided as N=8. Eachcomparator 30 receives one of eight comparator reference voltages Cref0to Cref7. Vout is input to a low-pass filter 31. The low-pass filter isconfigured to filter out any transients on Vout. The output of thelow-pass filter is provided as respective inputs to each of thecomparators. These may have the same values as Vref. Thus, Cref0 may beapproximately 1.19V and Cref7 may be approximately 1.12V.

A respective comparator will output a first value if the Vout is greaterthan Cref and a second value if Vout is less than or equal to Cref.Based on the outputs of the comparators, the digital block 32 provides aselection signal with a single active bit representing the referencevoltage to be selected. If comparator number y provides a first valueand comparator y+1 provides a second value, it can be determined thatVout is between the reference voltages used by comparators y and y+1.Accordingly, the digital gates 32 will be able to provide the selectionsignal with desired value. The digital block 32 may include an OR gateand an up/down counter.

Consider the following example of the operation of the circuit.

Assuming Vout=1.2V when the device is not demanding any current, andsince Cref0=1.19V and Cref7=1.12V, all comparators provide an outputequal to 0. The outputs of the comparators are provided to an OR gate,and the output of this OR gate is provided to an up/down counter. Thecounter counts down when the output is 0 and counts up when the outputis 1. In some embodiments the counter may be designed with overflowprotection.

In this example Ref0=1.2V and Ref7=1.27V. When there is no current Icoresourced by the ballast transistor MB, the output of OR gate is 0 andRef0 is selected. Assume the device starts consuming current, and Voutfalls by 10 mV to 1.19V. In this situation, the first comparator 30 awill provide an output which is equal to a logic one level. This willcause the output of OR gate to be logic level 1, which is also theselect signal of the up/down counter. The counter thus starts countingup and selects Ref1=1.21V. This increases the value of Vout by 10 mV andthe value of Vout becomes 1.20V. In this condition, the output of thefirst comparator 30 a becomes 0 and the counter counts down. This willcause Ref0=1.2V to be used. This will cause Vout to be equal to 1.19Vsuch that the first comparator 30 a output will be 1 repeating the abovecycle. Thus Vout oscillates between 1.19 & 1.20V. These two levels ofVout may be maintained irrespective of the amount of current provided bythe regulator.

Consider another example. If Vout drops to 1.16V (an offset of 40 mV),in this case the select signal of the up/down counter will remain 1until Ref3=1.24V is selected. When Ref 3 is selected, Vout again becomes1.2V and the counter select signal trips to 0. Finally Vout oscillatesbetween 1.19V & 1.20V with the selection of Ref 2 and Ref 3respectively.

Thus, if the device demands current, then Vout will start to fall. AsVout falls, one or more comparator output will change its state, thuscausing the reference voltage to be increased.

In some embodiments, the transient currents may be only a third of thetotal device consumption. If substantially all or most of the offset dueto the DC consumption of the device is cancelled (at least partially orcompletely) by the increase in the reference voltage, the undershoot orovershoot in the voltage due to the transient currents may be kept undercontrol.

Since the voltage is kept close to 1.2V, any current transient is unableto generate a device reset. For example, suppose the device is consuming100 mA DC current, which generates a DC offset of 50 mV. With someembodiments, this 50 mV DC offset is not significant. If suddenly thedevice demands another 100 mA current, then there will be an undershoot.Assuming an undershoot of 0.8 mV/mA, if the voltage was 1.2V the voltagewould become 1.2V−80 mV=1.12V, which is higher than 1.08V, which is theminimum allowed supply. In contrast, without the reference-selectcircuitry, the minimum voltage would be 1.2V−50 mV (DC offset)−80mV=1.07V, which is lower than the absolute minimum voltage limit. Thussome embodiments may allow a higher undershoot to be tolerated due tooffset compensation.

In some embodiments, the offset due to a leakage current may becancelled by the automatic increase in the reference voltage at highertemperatures.

Reference is made to FIG. 4, which shows an alternative arrangement tothat shown in FIG. 1. It is appreciated that like elements arereferenced using the same reference numbers. In the arrangement of FIG.4, the voltage regulator 16 is as shown in FIG. 1. However, a modifiedcontrol part 124 is provided.

The control part 124 of FIG. 4 includes a comparator 42, which has afirst input REF1 40 and a second input Vout 20. The output of thecomparator is provided to the up/down counter 44, which provides theselect signal 34, which is used in the voltage regulator as describedpreviously.

The comparator 42 compares the output voltage Vout with the referencevoltage REF1. The output of the comparator is provided to the up/downcounter. Depending on the result of the comparison, one of the taps ofthe selection signal is selected, which determines the reference voltageVref going to the regulator. If the device demands more current, thenthe Vout starts falling. As Vout falls below Ref1, the comparatoroutputs a select bit zero. This means that the up/down counter has tocount up and a next higher reference tap needs to be selected. Thecounter will keep on counting up until the selected bit becomes one. Atthis point, the counter starts counting down. When the counteroscillates between two states, this can be considered to be the stablestate of the regulator. The reference voltage to the comparator is fixedand should be within about 10 mv of the final value Vout which is to beregulated. If Vout is to be kept to 1.2V, then Ref1 may be fixed at1.19V.

In the embodiments of for example FIGS. 1 and 4, there are two closedloops. The first loop is that provided by the differential amplifier ofthe regulator with the feedback of Vout back into the input of thedifferential amplifier. There is a second closed loop which is used forthe selection of the regulator reference voltage. These two loops areworking at the same time. Accordingly, in an embodiment, the regulatorreference (Vref) loop switches slowly as compared to the first loop withthe differential amplifier. This provides system stability.

Reference is made to FIG. 5, which shows a method according to anembodiment.

In a first step, S1, the output voltage Vout is compared with thecontroller reference voltage or controller reference voltages. Forexample, in the arrangement of FIG. 3, Vout is compared with all of thecontroller reference voltages Crefn. In the case of the embodiment ofFIG. 4, Vout is compared with the single reference voltage Ref1.

In step S2, in dependence on the comparison, a counter is incremented ordecremented.

In step S3, a selection signal is output.

In step S4, the selection signal is used to control which regulatorreference voltage is used by the voltage regulator.

Some embodiments have been described in relation to an integratedcircuit. It is appreciated that some embodiments may be used with one ormore dies which may be packaged together. For example, an embodiment ofan integrated circuit that includes an embodiment of the above-describedLDO may include a computing circuit such as a microprocessor ormicrocontroller. And this integrated circuit may be coupled to one ormore other integrated circuits, such as a memory or pixel array. Andthese integrated circuits may be disposed on a same, or on respective,integrated-circuit dies.

Some embodiments compensate the offset due to DC current loads. This mayprovide advantages in terms of reducing the value, and thus the size, ofthe external stability capacitor 22. Consider the following example.Assume a regulator which has a DC offset of 35 mV with a deviceconsumption of 100 mA. The output stability capacitor has a value of 2.2uF. If the value of the output capacitor is to be reduced by a half to1.1 uF, then the gain of the above-described first control loop (i.e.,Vout, to the input of the amplifier 4, to the output of the amplifier,to the gate of the transistor 10, back to Vout) may need to be reducedby a half such that the system remains stable. The reduction in gainincreases the DC offset voltage to 70 mV. With some embodiments, thescheme may increase the reference going to the regulator by 70 mV (byusing the highest reference value) to compensate for the DC offset. Insome embodiments, the 35 mV DC offset may be compensated and the outputcapacitor is 2.2 uF. Alternatively the output capacitor may be reducedby half (1.1 uF) and there is compensation for the 70 mV DC offset.

It is appreciated that the values given in the above embodiments are byway of example only and in different embodiments, different values maybe used.

While this detailed description has set forth some embodiments, theremay exist other embodiments which differ from the described embodimentsaccording to various modifications and improvements.

From the foregoing it will be appreciated that, although specificembodiments have been described herein for purposes of illustration,various modifications may be made without deviating from the spirit andscope of the disclosure. Furthermore, where an alternative is disclosedfor a particular embodiment, this alternative may also apply to otherembodiments even if not specifically stated.

What is claimed is:
 1. A power supply, comprising: a regulator circuitconfigured to generate a regulated signal in response to a selected oneof a plurality of first reference signals provided on a reference nodeof the regulator circuit; a reference circuit configured tosimultaneously generate the plurality of first reference signals; and acontroller configured to compare each of a plurality of secondsimultaneously generated reference signals to the regulated signal and,in response to these comparisons, the controller configured to providethe selected one of the plurality of first reference signals on thereference node of the regulator circuit, wherein the controller furtherincludes: a plurality of comparators, each comparator configured tocompare the regulated signal to a corresponding one of the plurality ofsecond reference signals and to generate a corresponding output signalresponsive to the comparison; and a digital logic circuit coupled toreceive the respective output signals from the plurality of comparators,the digital logic circuit further configured to generate a count valuebased on the values of the output signals and configured to provide aselected one of the plurality of first reference signals to theregulator circuit based upon the count value.
 2. The power supply ofclaim 1 wherein: the regulated signal includes a regulated voltage; andthe first and second reference signals are reference voltages.
 3. Thepower supply of claim 2 wherein the regulator circuit includes alow-dropout-regulator circuit.
 4. The power supply of claim 1, whereinthe digital logic circuit further comprises: an OR gate having aplurality of inputs, each input coupled to the output of a respectiveone of the comparators and the OR gate having an output; and a countercoupled to the output of the OR gate and configured to generate a countvalue in response to a value of a logic signal at the output of the ORgate, the controller providing the selected one of the plurality offirst reference signals to the regulator circuit responsive to the countvalue.
 5. The power supply of claim 1, further comprising: wherein theregulator circuit includes a node configured to carry the regulatedsignal; and a compensation capacitor coupled to the node.
 6. A system,comprising: a first integrated circuit including: a reference voltagecircuit configured to concurrently generate a plurality of firstreference voltage signals; and a voltage regulator circuit configured togenerate a regulated voltage signal in response to a selected one of theplurality of first reference voltage signals provided on a referencenode of the regulator circuit; and a controller coupled to the voltageregulator circuit and the reference voltage circuit, the controllerconfigured to compare each of a plurality of concurrently generatedsecond reference voltage signals to the regulated voltage signal and, inresponse to these comparisons, the controller configured to provide oneof the plurality of first reference voltage signals as the selectedreference voltage signal on the reference node of the regulator circuit,wherein the controller further includes, a plurality of comparators,each comparator configured to compare the regulated signal to acorresponding one of the plurality of second reference signals and togenerate a corresponding output signal responsive to the comparison; anOR gate having a plurality of inputs, each input coupled to the outputof a respective one of the comparators and the OR gate having an output;and a counter coupled to the output of the OR gate and configured togenerate a count value in response to a value of a logic signal at theoutput of the OR gate, the controller providing the selected one of theplurality of first reference signals to the regulator circuit responsiveto the count value; and a second integrated circuit coupled to the firstintegrated circuit.
 7. The system of claim 6 wherein one of the firstand second integrated circuits includes a computing circuit.
 8. Thesystem of claim 6 wherein the first and second integrated circuits aredisposed on a same die.
 9. The system of claim 6 wherein the first andsecond integrated circuits are disposed on respective dies.
 10. Thesystem of claim 6 wherein a portion of the regulator is disposed outsideof the first integrated circuit.
 11. A method for a voltage regulator,comprising: selecting a reference voltage signal; regulating a voltagesignal in response to the selected reference voltage signal; generatingat the same time a plurality of candidate reference voltage signals;generating at the same time a plurality of comparison reference voltagesignals; comparing each of the comparison reference voltage signals tothe regulated voltage signal; and providing on a reference node theselected reference voltage signal from among the plurality of candidatereference voltage signals responsive to the comparisons, whereinproviding on the reference node the selected voltage signal includes:generating a comparison voltage signal responsive to the comparing ofeach of the comparison reference voltage signals to the regulatedvoltage signal; performing a logical OR operation on the generatedcomparison voltage signals to generate a logic output signal; adjustinga count value responsive to the logic output signal; and choosing theselected reference voltage signal responsive to adjusted count value.